Biodiesel fuel technology is being developed throughout the world as a way to decrease reliance on crude oil, to boost local economies, and to reduce carbon dioxide emissions by using a renewable fuel source. Biodiesel fuel is comprised of methyl and/or ethyl esters of fatty acids, and is typically derived by the transesterification of vegetable oils and/or animal fats with methanol or ethanol, catalyzed by a base such as potassium hydroxide. The resulting by-product, crude glycerol, includes the potassium hydroxide as well as any water present in the potassium hydroxide.
Any fatty acids present in the triglycerides must be neutralized with the basic catalyst. As a result, if the triglycerides include even one percent fatty acids, the amount of salt and water in the glycerol increases significantly. Because glycerol is only about ten percent of the reaction volume, an additional one percent of potassium hydroxide in effect doubles the amount of salt and water in the crude glycerol product, relative to the use of one percent by volume of the basic catalyst.
The glycerol by-product can be used to prepare other value added products, including glycerol ethers. These are typically prepared by the acid-catalyzed etherification of glycerol with isobutylene. Because the glycerol ether chemistry is acid catalyzed, the base must be neutralized. Also, because isobutylene reacts with water to product t-butanol, the water must be removed as well.
Because it is relatively expensive to purify the crude glycerol to prepare it for third party usage, the crude glycerol from biodiesel production typically has a low value. Accordingly, it would be beneficial to provide processes for producing biodiesel fuel that provide glycerol in a more pure form, and/or for purifying the crude glycerol in a way that provides additional yields of biofuel, ideally in a manner which improves the resulting biodiesel fuel synthesis as well. The present invention provides such processes.